Term long-run industry supply curve Definition: The relation between market price and the quantity supplied by all firms in a perfectly competitive industry after the industry as completed its long-run adjustment. The long-run industry supply curve effectively traces out a series of equilibrium prices and quantities the reflect long-run adjustments of a perfectly competitive industry to demand shocks. This long-run adjustment can take one of three paths: increasing, decreasing, and constant. These three adjustment paths indicate an increasing-cost industry, decreasing-cost industry, and constant-cost industry, respectively.